This invention relates to a fuel assembly for nuclear reactors, and more particularly, to a nuclear reactor fuel assembly in which a plurality of fuel rods are spaced from one another by a spacer and contained in a channel box.
A Zr-Nb alloy which is composed of 0.5-5 wt % Nb and balance Zr is known as material for parts of BWR and PWR and disclosed in Japanese Patent Laid-Open No. 47-42220 (1972). This Japanese Patent Laid-Open discloses that welds of the Zr-Nb alloy corrode in a high-temperature water to produce a white oxide film thereby to have an accelerated corrosivity, and that the Zr-Nb alloy forms a black oxide film when heated at a temperature of 450.degree.-650.degree. C. after welding thereby to have corrosion resistance.
On the other hand, it is reported that a Zr-Nb alloy including 2.5 wt % Nb produces a white corrosion under an environment of high-temperature and high-pressure water when subjected to heat treatment after welding. The information is disclosed in Proceedings of the International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors, Myrtle Beach, S. C. Aug.22-25, 1983, pages 274-294.
The above-mentioned two prior arts disclose the contraries concerning the effect of the heat treatment for preventing a weld and its heat affected zone of the Zr-Nb alloy from producing white corrosion or white oxide film. Thus, any effective means for prevention of the white corrosion at the weld and the heat affected zone has not been established.